Schizophrenia is a complex disorder, perhaps a complex of disorders. Sometimes people who separate and categorize concepts miss the fact that these possibilities are not necessarily mutually exclusive. No one explanation of the biological cause of the disease necessarily must invalidate other explanations.

A Chemical Hypothesis

One of the oldest biochemical explanations of what causes schizophrenia is based on our understanding of how antipsychotic medications work. In short, it says there is something wrong somewhere along the chemical messenger pathway. Somehow, neurons located in key parts of the brain receive abnormal signals or do not effectively process chemical signals from other neurons. This breakdown or miscommunication somehow results in the myriad symptoms seen in schizophrenia. In theory, straightening out these signaling systems should correct the problem. Currently available medications can do this to some extent, but only partially and imperfectly. Perhaps we haven't developed drugs that target the chemical abnormality effectively enough, or perhaps there is more to the underlying problem in schizophrenia than described by this scheme.

A Genetic Hypothesis

This explanation emphasizes the inheritance of genes that increase a person's susceptibility to developing some form of schizophrenia. This hypothesis has been strengthened in recent years with the identification of genes that are suspected of playing a role in the disease. Perhaps the drugs now used to treat schizophrenia target some of the proteins made by these very genes. If we could pin down exactly which genes are associated with schizophrenia, it might someday be possible to design drugs that target them specifically.

A Brain Connection Hypothesis

This explanation suggests that schizophrenia results from faulty wiring or connections between crucial areas of the brain. Such improper wiring probably occurs early in life, making schizophrenia a neurodevelopmental disorder.

Multiple events could account for changes in brain connections. This hypothesis fits easily into a combined hypothesis that might explain the biological basis of the disease: A genetic predisposition makes some people sensitive to factors such as prenatal or childhood infections, nutritional deficiencies, or exposure to toxins and/or psychological stresses. These factors affect brain development, leading to faulty connections and structural and chemical abnormalities.

The drugs now available may be capable of acting on only one or a few of the resulting functional abnormalities. Furthermore, the medications may do so imperfectly.

Other Explanations

In the past, some psychologists have suggested that many of the problems experienced by people with schizophrenia can be traced to their reactions to stress, social pressures, family dynamics, labeling, or upbringing. Data supporting these views is very limited compared to data supporting biological theories. It is likely that psychological factors — reactions to stress, for example — are a factor in the development and expression of the disorder's symptoms. Explanations that rely purely on psychological or sociocultural factors that fail to consider known biological factors, however, remain unconvincing to most scientists and others who are familiar with the disease.